Disease: Chytrid

Chytridiomycosis is an infectious disease caused by a fungus. It appears to be a major factor in dramatic amphibian declines in many parts of the world. It is particularly linked with the decline, and extinction, of tropical species.

The disease is caused by a fungus – and is often referred to as chytrid or the chytrid fungus – which can potentially kill all of the individuals in a population.

The disease is thought to be a major factor in the decline and extinction of many amphibian species across the world, particularly in Australia, the Caribbean and North, Central and South America.

It is thought it affects the animals skin tissue and causes problems with respiration and water uptake. As the fungus only affects keratinised tissue it does not cause the death of tadpoles – they only have keratin in their mouthparts and so carry the disease until they metamorphose.

In the UK, toads appear more susceptible than other amphibian species. It is thought the disease has been introduced through imported non-native amphibians.

The disease has had a lot of press coverage which is excellent for raising awareness but it is important to stress that if you are finding dead amphibians it is far more likely there is another cause.

Chytrid has been found at 19 locations in the UK. It was reported for the first time in native amphibians in 2005, at a site in the southeast of England. The disease was later found at two separate locations in northern England which prompted further study. In 2008 Natural England and the Institute of Zoology began widespread disease monitoring of other sites in the UK to assess the threat that the disease may pose to our native amphibian species. The vast majority of samples were negative for chytrid, but there were some positives which were quite widespread.What you can do

As tadpoles only carry the disease in many cases, the only dead amphibians are those that have recently metamorphosed, although dead adults might also be found, usually away from the pond. Here are some of the things to look out for:

Large numbers of dead toadlets, froglets (May-June) or newtlets (June to September), just after metamorphosis.

Skin flaking.

Lethargy.

Dead amphibians with no obvious cause of death or signs of disease.

The mass mortality at metamorphosis is the main thing to watch out for. The other symptoms may not develop and may be difficult to observe without closer inspection.

Occasionally you may see dead amphibians with a white fungus on them, or bodies in the pond with skin problems, but these individuals have not been affected by chytrid. There are various other diseases that can affect amphibians and often ‘symptoms’ have occurred after death.